1. Field of the Invention
This invention relates to a driving control device, an optical apparatus and a driving control method for accurately driving a driven body which is arranged to be driven by an actuator.
2. Description of Related Art
Picture taking apparatuses having an automatic focusing (AF) function, such as single-lens reflex cameras, video cameras, etc., and optical apparatuses and picture taking accessories, such as lenses and flash devices, have recently come to be provided with actuators, such as a DC motor, a stepping motor and a vibration wave motor. Their multifunctional and high-performance capabilities thus have advanced during recent years.
Generally, the internal mechanical arrangements of these equipments are caused to become complex by the actuators, reduction gears, cams, etc. Backlash in a gear train, play of fitting engagement and the like increase accordingly as the complexity of the internal mechanical arrangement increases. In the case of a camera having an automatic focusing mechanism, for example, the complexity of the mechanical arrangement causes deviations of focus and those of film transporting positions.
These problems may be made less serious to a certain extent by improving the precision of parts of the mechanical arrangement. It is, however, hardly possible to completely remove the play from a mechanical moving mechanism. Besides, an improvement in precision of parts causes an increase in manufacturing cost. Further, the adverse effect of the play of parts may be also lessened by including a mechanical canceling arrangement in the gear train. However, that arrangement still leaves problems unsolved with respect to an increase in cost and unevenness in precision of the parts.
To mitigate the adverse effect of the play of parts on the driving control for an actuator, it has been practiced to cancel the play by varying an amount of driving in driving a focusing unit of an automatic focusing lens, for example, if there is any possibility that the direction of the driving might be affected by mechanical play.
FIG. 1 shows the mechanism of operation of the conventional automatic focusing lens which is provided with a driving control device arranged in a system as mentioned above. Referring to FIG. 1, a focusing unit 100 is arranged to hold a focusing lens and to be movable in parallel to an optical axis X--X. The locus of the motion of the focusing unit 100 is defined jointly by a cam follower (roller) 101 which is fixed to the focusing unit 100 and a cam 102 which is arranged to revolve on the optical axis. When the cam follower 101 is at an upper part of the cam 102, as shown in FIG. 1, the focusing unit 100 is in a nearest distance position. When the cam 102 revolves in the direction of an arrow indicated by a full line, i.e., toward the right, the focusing unit 100 moves in the direction of an arrow indicated by a dotted line according to the shape of the cam 102.
FIGS. 2A and 2B roughly show the relation of the cam follower 101 to the cam 102. Referring to FIG. 2A, since each of the cam 102 and the cam follower 101 is a moving member, it is inevitable to have some mechanical play between them. When the cam 102 revolves, the cam follower 101 moves in a state of being pulled into contact with one side face of the cam 102 due to the play. In a case where the cam 102 is to be moved in a direction reverse to the direction in which the cam 102 has been last moved, even if the cam 102 begins moving, the cam follower 101 cannot be moved instantly until a distance of play is crossed, as shown in FIG. 2B, which is an enlarged view of FIG. 2A.
The amount of play "g" between the cam 102 and the cam follower 101 is then computed and obtained from the mechanical play "d" of fitting engagement and the inclination sin .theta. of the cam 102. Thus, the amount of play "g" is obtained by the computing formula of "g=d/sin .theta.". As shown in FIGS. 3A and 3B, the inclination sin .theta. of the cam 102 included in this formula causes the amount of play "g" to vary to give a relation of "g.gtoreq.d" when the inclination sin .theta. is close to 90 degrees.
The relation between the cam 102 and the cam follower 101 is close to a state shown in FIGS. 2A and 2B when the focusing unit 100 is located at an infinity distance position shown in FIG. 1, and is close to a state shown in FIGS. 3A and 3B when the focusing unit 100 is located at the nearest distance position shown in FIG. 1. In other words, the amount of play "g" between the cam 102 and the cam follower 101 varies with the position of the focusing unit 100 in the direction of the optical axis.
Reduction in size and enhancement in performance of the apparatuses using the driving control devices of the above-stated kind are expected to be furthered in the future. The above-stated complexity of the internal mechanical arrangement of parts is thus expected to be also furthered to diversify the state and the amount of play resulting from backlash and play. The arrangement of the convention driving control device described above is considered to be hardly capable of adequately coping with this trend because it leaves the amount of play in a fixed state.